///*
// * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
// * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
// *
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// */
//package concurrent.future;
//import java.lang.ref.*;
//import java.util.Objects;
//import java.util.concurrent.atomic.AtomicInteger;
//import java.util.function.Supplier;
//
//public class MyThreadLocal<T> {
//    /**
//     * ThreadLocals rely on per-thread linear-probe hash maps attached
//     * to each thread (Thread.threadLocals and
//     * inheritableThreadLocals).  The ThreadLocal objects act as keys,
//     * searched via threadLocalHashCode.  This is a custom hash code
//     * (useful only within ThreadLocalMaps) that eliminates collisions
//     * in the common case where consecutively constructed ThreadLocals
//     * are used by the same threads, while remaining well-behaved in
//     * less common cases.
//     */
//    private final int threadLocalHashCode = nextHashCode();
//
//    /**
//     * The next hash code to be given out. Updated atomically. Starts at
//     * zero.
//     */
//    private static AtomicInteger nextHashCode =
//            new AtomicInteger();
//
//    /**
//     * The difference between successively generated hash codes - turns
//     * implicit sequential thread-local IDs into near-optimally spread
//     * multiplicative hash values for power-of-two-sized tables.
//     */
//    private static final int HASH_INCREMENT = 0x61c88647;
//
//    /**
//     * Returns the next hash code.
//     */
//    private static int nextHashCode() {
//        return nextHashCode.getAndAdd(HASH_INCREMENT);
//    }
//
//    /**
//     * Returns the current thread's "initial value" for this
//     * thread-local variable.  This method will be invoked the first
//     * time a thread accesses the variable with the {@link #get}
//     * method, unless the thread previously invoked the {@link #set}
//     * method, in which case the {@code initialValue} method will not
//     * be invoked for the thread.  Normally, this method is invoked at
//     * most once per thread, but it may be invoked again in case of
//     * subsequent invocations of {@link #remove} followed by {@link #get}.
//     *
//     * <p>This implementation simply returns {@code null}; if the
//     * programmer desires thread-local variables to have an initial
//     * value other than {@code null}, {@code ThreadLocal} must be
//     * subclassed, and this method overridden.  Typically, an
//     * anonymous inner class will be used.
//     *
//     * @return the initial value for this thread-local
//     */
//    protected T initialValue() {
//        return null;
//    }
//
//    /**
//     * Creates a thread local variable. The initial value of the variable is
//     * determined by invoking the {@code get} method on the {@code Supplier}.
//     *
//     * @param <S> the type of the thread local's value
//     * @param supplier the supplier to be used to determine the initial value
//     * @return a new thread local variable
//     * @throws NullPointerException if the specified supplier is null
//     * @since 1.8
//     */
//    public static <S> ThreadLocal<S> withInitial(Supplier<? extends S> supplier) {
//        return new SuppliedThreadLocal<>(supplier);
//    }
//
//    /**
//     * Creates a thread local variable.
//     * @see #withInitial(java.util.function.Supplier)
//     */
//    public ThreadLocal() {
//    }
//
//    /**
//     * Returns the value in the current thread's copy of this
//     * thread-local variable.  If the variable has no value for the
//     * current thread, it is first initialized to the value returned
//     * by an invocation of the {@link #initialValue} method.
//     *
//     * @return the current thread's value of this thread-local
//     */
//    public T get() {
//        Thread t = Thread.currentThread();
//        ThreadLocalMap map = getMap(t);
//        if (map != null) {
//            ThreadLocalMap.Entry e = map.getEntry(this);
//            if (e != null) {
//                @SuppressWarnings("unchecked")
//                T result = (T)e.value;
//                return result;
//            }
//        }
//        return setInitialValue();
//    }
//
//    /**
//     * Variant of set() to establish initialValue. Used instead
//     * of set() in case user has overridden the set() method.
//     *
//     * @return the initial value
//     */
//    private T setInitialValue() {
//        T value = initialValue();
//        Thread t = Thread.currentThread();
//        ThreadLocalMap map = getMap(t);
//        if (map != null)
//            map.set(this, value);
//        else
//            createMap(t, value);
//        return value;
//    }
//
//    /**
//     * Sets the current thread's copy of this thread-local variable
//     * to the specified value.  Most subclasses will have no need to
//     * override this method, relying solely on the {@link #initialValue}
//     * method to set the values of thread-locals.
//     *
//     * @param value the value to be stored in the current thread's copy of
//     *        this thread-local.
//     */
//    public void set(T value) {
//        Thread t = Thread.currentThread();
//        ThreadLocalMap map = getMap(t);
//        if (map != null)
//            map.set(this, value);
//        else
//            createMap(t, value);
//    }
//
//    /**
//     * Removes the current thread's value for this thread-local
//     * variable.  If this thread-local variable is subsequently
//     * {@linkplain #get read} by the current thread, its value will be
//     * reinitialized by invoking its {@link #initialValue} method,
//     * unless its value is {@linkplain #set set} by the current thread
//     * in the interim.  This may result in multiple invocations of the
//     * {@code initialValue} method in the current thread.
//     *
//     * @since 1.5
//     */
//    public void remove() {
//        ThreadLocalMap m = getMap(Thread.currentThread());
//        if (m != null)
//            m.remove(this);
//    }
//
//    /**
//     * Get the map associated with a ThreadLocal. Overridden in
//     * InheritableThreadLocal.
//     *
//     * @param  t the current thread
//     * @return the map
//     */
//    ThreadLocalMap getMap(Thread t) {
//        return t.threadLocals;
//    }
//
//    /**
//     * Create the map associated with a ThreadLocal. Overridden in
//     * InheritableThreadLocal.
//     *
//     * @param t the current thread
//     * @param firstValue value for the initial entry of the map
//     */
//    void createMap(Thread t, T firstValue) {
//        t.threadLocals = new ThreadLocalMap(this, firstValue);
//    }
//
//    /**
//     * Factory method to create map of inherited thread locals.
//     * Designed to be called only from Thread constructor.
//     *
//     * @param  parentMap the map associated with parent thread
//     * @return a map containing the parent's inheritable bindings
//     */
//    static ThreadLocalMap createInheritedMap(ThreadLocalMap parentMap) {
//        return new ThreadLocalMap(parentMap);
//    }
//
//    /**
//     * Method childValue is visibly defined in subclass
//     * InheritableThreadLocal, but is internally defined here for the
//     * sake of providing createInheritedMap factory method without
//     * needing to subclass the map class in InheritableThreadLocal.
//     * This technique is preferable to the alternative of embedding
//     * instanceof tests in methods.
//     */
//    T childValue(T parentValue) {
//        throw new UnsupportedOperationException();
//    }
//
//    /**
//     * An extension of ThreadLocal that obtains its initial value from
//     * the specified {@code Supplier}.
//     */
//    static final class SuppliedThreadLocal<T> extends ThreadLocal<T> {
//
//        private final Supplier<? extends T> supplier;
//
//        SuppliedThreadLocal(Supplier<? extends T> supplier) {
//            this.supplier = Objects.requireNonNull(supplier);
//        }
//
//        @Override
//        protected T initialValue() {
//            return supplier.get();
//        }
//    }
//
//    /**
//     * ThreadLocalMap is a customized hash map suitable only for
//     * maintaining thread local values. No operations are exported
//     * outside of the ThreadLocal class. The class is package private to
//     * allow declaration of fields in class Thread.  To help deal with
//     * very large and long-lived usages, the hash table entries use
//     * WeakReferences for keys. However, since reference queues are not
//     * used, stale entries are guaranteed to be removed only when
//     * the table starts running out of space.
//     */
//    static class ThreadLocalMap {
//
//        /**
//         * The entries in this hash map extend WeakReference, using
//         * its main ref field as the key (which is always a
//         * ThreadLocal object).  Note that null keys (i.e. entry.get()
//         * == null) mean that the key is no longer referenced, so the
//         * entry can be expunged from table.  Such entries are referred to
//         * as "stale entries" in the code that follows.
//         */
//        static class Entry extends WeakReference<ThreadLocal<?>> {
//            /** The value associated with this ThreadLocal. */
//            Object value;
//
//            Entry(ThreadLocal<?> k, Object v) {
//                super(k);
//                value = v;
//            }
//        }
//
//        /**
//         * The initial capacity -- MUST be a power of two.
//         */
//        private static final int INITIAL_CAPACITY = 16;
//
//        /**
//         * The table, resized as necessary.
//         * table.length MUST always be a power of two.
//         */
//        private Entry[] table;
//
//        /**
//         * The number of entries in the table.
//         */
//        private int size = 0;
//
//        /**
//         * The next size value at which to resize.
//         */
//        private int threshold; // Default to 0
//
//        /**
//         * Set the resize threshold to maintain at worst a 2/3 load factor.
//         */
//        private void setThreshold(int len) {
//            threshold = len * 2 / 3;
//        }
//
//        /**
//         * Increment i modulo len.
//         */
//        private static int nextIndex(int i, int len) {
//            return ((i + 1 < len) ? i + 1 : 0);
//        }
//
//        /**
//         * Decrement i modulo len.
//         */
//        private static int prevIndex(int i, int len) {
//            return ((i - 1 >= 0) ? i - 1 : len - 1);
//        }
//
//        /**
//         * Construct a new map initially containing (firstKey, firstValue).
//         * ThreadLocalMaps are constructed lazily, so we only create
//         * one when we have at least one entry to put in it.
//         */
//        ThreadLocalMap(ThreadLocal<?> firstKey, Object firstValue) {
//            table = new Entry[INITIAL_CAPACITY];
//            int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1);
//            table[i] = new Entry(firstKey, firstValue);
//            size = 1;
//            setThreshold(INITIAL_CAPACITY);
//        }
//
//        /**
//         * Construct a new map including all Inheritable ThreadLocals
//         * from given parent map. Called only by createInheritedMap.
//         *
//         * @param parentMap the map associated with parent thread.
//         */
//        private ThreadLocalMap(ThreadLocalMap parentMap) {
//            Entry[] parentTable = parentMap.table;
//            int len = parentTable.length;
//            setThreshold(len);
//            table = new Entry[len];
//
//            for (int j = 0; j < len; j++) {
//                Entry e = parentTable[j];
//                if (e != null) {
//                    @SuppressWarnings("unchecked")
//                    ThreadLocal<Object> key = (ThreadLocal<Object>) e.get();
//                    if (key != null) {
//                        Object value = key.childValue(e.value);
//                        Entry c = new Entry(key, value);
//                        int h = key.threadLocalHashCode & (len - 1);
//                        while (table[h] != null)
//                            h = nextIndex(h, len);
//                        table[h] = c;
//                        size++;
//                    }
//                }
//            }
//        }
//
//        /**
//         * Get the entry associated with key.  This method
//         * itself handles only the fast path: a direct hit of existing
//         * key. It otherwise relays to getEntryAfterMiss.  This is
//         * designed to maximize performance for direct hits, in part
//         * by making this method readily inlinable.
//         *
//         * @param  key the thread local object
//         * @return the entry associated with key, or null if no such
//         */
//        private Entry getEntry(ThreadLocal<?> key) {
//            int i = key.threadLocalHashCode & (table.length - 1);
//            Entry e = table[i];
//            if (e != null && e.get() == key)
//                return e;
//            else
//                return getEntryAfterMiss(key, i, e);
//        }
//
//        /**
//         * Version of getEntry method for use when key is not found in
//         * its direct hash slot.
//         *
//         * @param  key the thread local object
//         * @param  i the table index for key's hash code
//         * @param  e the entry at table[i]
//         * @return the entry associated with key, or null if no such
//         */
//        private Entry getEntryAfterMiss(ThreadLocal<?> key, int i, Entry e) {
//            Entry[] tab = table;
//            int len = tab.length;
//
//            while (e != null) {
//                ThreadLocal<?> k = e.get();
//                if (k == key)
//                    return e;
//                if (k == null)
//                    expungeStaleEntry(i);
//                else
//                    i = nextIndex(i, len);
//                e = tab[i];
//            }
//            return null;
//        }
//
//        /**
//         * Set the value associated with key.
//         *
//         * @param key the thread local object
//         * @param value the value to be set
//         */
//        private void set(ThreadLocal<?> key, Object value) {
//
//            // We don't use a fast path as with get() because it is at
//            // least as common to use set() to create new entries as
//            // it is to replace existing ones, in which case, a fast
//            // path would fail more often than not.
//
//            Entry[] tab = table;
//            int len = tab.length;
//            int i = key.threadLocalHashCode & (len-1);
//
//            for (Entry e = tab[i];
//                 e != null;
//                 e = tab[i = nextIndex(i, len)]) {
//                ThreadLocal<?> k = e.get();
//
//                if (k == key) {
//                    e.value = value;
//                    return;
//                }
//
//                if (k == null) {
//                    replaceStaleEntry(key, value, i);
//                    return;
//                }
//            }
//
//            tab[i] = new Entry(key, value);
//            int sz = ++size;
//            if (!cleanSomeSlots(i, sz) && sz >= threshold)
//                rehash();
//        }
//
//        /**
//         * Remove the entry for key.
//         */
//        private void remove(ThreadLocal<?> key) {
//            Entry[] tab = table;
//            int len = tab.length;
//            int i = key.threadLocalHashCode & (len-1);
//            for (Entry e = tab[i];
//                 e != null;
//                 e = tab[i = nextIndex(i, len)]) {
//                if (e.get() == key) {
//                    e.clear();
//                    expungeStaleEntry(i);
//                    return;
//                }
//            }
//        }
//
//        /**
//         * Replace a stale entry encountered during a set operation
//         * with an entry for the specified key.  The value passed in
//         * the value parameter is stored in the entry, whether or not
//         * an entry already exists for the specified key.
//         *
//         * As a side effect, this method expunges all stale entries in the
//         * "run" containing the stale entry.  (A run is a sequence of entries
//         * between two null slots.)
//         *
//         * @param  key the key
//         * @param  value the value to be associated with key
//         * @param  staleSlot index of the first stale entry encountered while
//         *         searching for key.
//         */
//        private void replaceStaleEntry(ThreadLocal<?> key, Object value,
//                                       int staleSlot) {
//            Entry[] tab = table;
//            int len = tab.length;
//            Entry e;
//
//            // Back up to check for prior stale entry in current run.
//            // We clean out whole runs at a time to avoid continual
//            // incremental rehashing due to garbage collector freeing
//            // up refs in bunches (i.e., whenever the collector runs).
//            int slotToExpunge = staleSlot;
//            for (int i = prevIndex(staleSlot, len);
//                 (e = tab[i]) != null;
//                 i = prevIndex(i, len))
//                if (e.get() == null)
//                    slotToExpunge = i;
//
//            // Find either the key or trailing null slot of run, whichever
//            // occurs first
//            for (int i = nextIndex(staleSlot, len);
//                 (e = tab[i]) != null;
//                 i = nextIndex(i, len)) {
//                ThreadLocal<?> k = e.get();
//
//                // If we find key, then we need to swap it
//                // with the stale entry to maintain hash table order.
//                // The newly stale slot, or any other stale slot
//                // encountered above it, can then be sent to expungeStaleEntry
//                // to remove or rehash all of the other entries in run.
//                if (k == key) {
//                    e.value = value;
//
//                    tab[i] = tab[staleSlot];
//                    tab[staleSlot] = e;
//
//                    // Start expunge at preceding stale entry if it exists
//                    if (slotToExpunge == staleSlot)
//                        slotToExpunge = i;
//                    cleanSomeSlots(expungeStaleEntry(slotToExpunge), len);
//                    return;
//                }
//
//                // If we didn't find stale entry on backward scan, the
//                // first stale entry seen while scanning for key is the
//                // first still present in the run.
//                if (k == null && slotToExpunge == staleSlot)
//                    slotToExpunge = i;
//            }
//
//            // If key not found, put new entry in stale slot
//            tab[staleSlot].value = null;
//            tab[staleSlot] = new Entry(key, value);
//
//            // If there are any other stale entries in run, expunge them
//            if (slotToExpunge != staleSlot)
//                cleanSomeSlots(expungeStaleEntry(slotToExpunge), len);
//        }
//
//        /**
//         * Expunge a stale entry by rehashing any possibly colliding entries
//         * lying between staleSlot and the next null slot.  This also expunges
//         * any other stale entries encountered before the trailing null.  See
//         * Knuth, Section 6.4
//         *
//         * @param staleSlot index of slot known to have null key
//         * @return the index of the next null slot after staleSlot
//         * (all between staleSlot and this slot will have been checked
//         * for expunging).
//         */
//        private int expungeStaleEntry(int staleSlot) {
//            Entry[] tab = table;
//            int len = tab.length;
//
//            // expunge entry at staleSlot
//            tab[staleSlot].value = null;
//            tab[staleSlot] = null;
//            size--;
//
//            // Rehash until we encounter null
//            Entry e;
//            int i;
//            for (i = nextIndex(staleSlot, len);
//                 (e = tab[i]) != null;
//                 i = nextIndex(i, len)) {
//                ThreadLocal<?> k = e.get();
//                if (k == null) {
//                    e.value = null;
//                    tab[i] = null;
//                    size--;
//                } else {
//                    int h = k.threadLocalHashCode & (len - 1);
//                    if (h != i) {
//                        tab[i] = null;
//
//                        // Unlike Knuth 6.4 Algorithm R, we must scan until
//                        // null because multiple entries could have been stale.
//                        while (tab[h] != null)
//                            h = nextIndex(h, len);
//                        tab[h] = e;
//                    }
//                }
//            }
//            return i;
//        }
//
//        /**
//         * Heuristically scan some cells looking for stale entries.
//         * This is invoked when either a new element is added, or
//         * another stale one has been expunged. It performs a
//         * logarithmic number of scans, as a balance between no
//         * scanning (fast but retains garbage) and a number of scans
//         * proportional to number of elements, that would find all
//         * garbage but would cause some insertions to take O(n) time.
//         *
//         * @param i a position known NOT to hold a stale entry. The
//         * scan starts at the element after i.
//         *
//         * @param n scan control: {@code log2(n)} cells are scanned,
//         * unless a stale entry is found, in which case
//         * {@code log2(table.length)-1} additional cells are scanned.
//         * When called from insertions, this parameter is the number
//         * of elements, but when from replaceStaleEntry, it is the
//         * table length. (Note: all this could be changed to be either
//         * more or less aggressive by weighting n instead of just
//         * using straight log n. But this version is simple, fast, and
//         * seems to work well.)
//         *
//         * @return true if any stale entries have been removed.
//         */
//        private boolean cleanSomeSlots(int i, int n) {
//            boolean removed = false;
//            Entry[] tab = table;
//            int len = tab.length;
//            do {
//                i = nextIndex(i, len);
//                Entry e = tab[i];
//                if (e != null && e.get() == null) {
//                    n = len;
//                    removed = true;
//                    i = expungeStaleEntry(i);
//                }
//            } while ( (n >>>= 1) != 0);
//            return removed;
//        }
//
//        /**
//         * Re-pack and/or re-size the table. First scan the entire
//         * table removing stale entries. If this doesn't sufficiently
//         * shrink the size of the table, double the table size.
//         */
//        private void rehash() {
//            expungeStaleEntries();
//
//            // Use lower threshold for doubling to avoid hysteresis
//            if (size >= threshold - threshold / 4)
//                resize();
//        }
//
//        /**
//         * Double the capacity of the table.
//         */
//        private void resize() {
//            Entry[] oldTab = table;
//            int oldLen = oldTab.length;
//            int newLen = oldLen * 2;
//            Entry[] newTab = new Entry[newLen];
//            int count = 0;
//
//            for (int j = 0; j < oldLen; ++j) {
//                Entry e = oldTab[j];
//                if (e != null) {
//                    ThreadLocal<?> k = e.get();
//                    if (k == null) {
//                        e.value = null; // Help the GC
//                    } else {
//                        int h = k.threadLocalHashCode & (newLen - 1);
//                        while (newTab[h] != null)
//                            h = nextIndex(h, newLen);
//                        newTab[h] = e;
//                        count++;
//                    }
//                }
//            }
//
//            setThreshold(newLen);
//            size = count;
//            table = newTab;
//        }
//
//        /**
//         * Expunge all stale entries in the table.
//         */
//        private void expungeStaleEntries() {
//            Entry[] tab = table;
//            int len = tab.length;
//            for (int j = 0; j < len; j++) {
//                Entry e = tab[j];
//                if (e != null && e.get() == null)
//                    expungeStaleEntry(j);
//            }
//        }
//    }
//}
